1. Field of the Invention
The present invention relates to a process for preparing a vinyl derivative of a Bronsted acid by the transvinylation reaction of a vinyl derivative of a first Bronsted acid with a second Bronsted acid, and more particularly, to such a transvinylation process by reactive distillation of the transvinylation reaction mixture.
2. Description of the Prior Art
Transvinylation or vinyl interchange technology is well known. The reaction can be illustrated by the reaction of a vinyl-containing compound (R'CH=CH.sub.2) with an active hydrogen containing compound (RX), as in the following: ##STR1## wherein R is carboxyl, amino, aroxy, alkoxy, and the like; X is hydrogen, hydroxyl, alkyl, aryl, and the like; and R' is carboxyl, amino, alkyl, substituted alkyl, aryl or substituted aryl.
Adelman, Journal Organic Chemistry, 14, pp. 1057-1077, 1949, at p. 1057, termed transvinylation "the `Vinyl Interchange` Reaction, to differentiate it from typical ester interchange and ester-acid interchange reactions . . . " Adelman noted several advantages for preparing vinyl monomers by transvinylation, including, for example, the very mild reaction conditions, the low yields of by-products and the relatively higher yield of monomers of greater purity and activity compared to monomers prepared by the reaction of acetylene with acids.
Adelman also noted that vinyl esters of dibasic acids were prepared much more easily by vinyl interchange than through the acetylene route, and he demonstrated that the reaction of vinyl acetate catalyzed with mercuric salts was not restricted to carboxylic acids, but would occur with other compounds containing active hydrogen, such as acetoacetic ester and glycolic esters.
Other researchers have demonstrated the versatility of the transvinylation reaction and its applicability to a wide range of Bronsted acids and derivatives of Bronsted acids, using a wide variety of different catalysts. For example, McKeon, et al., Tetrahedron, 28 pp. 227-232 (1972) show the vinyl interchange reaction between a vinyl ether and an alcohol using a palladium catalyst. Other sources report the transvinylation reaction between vinyl chloride and a carboxylic acid.
The literature suggests that the preferred catalysts for transvinylation reactions have been mercury and palladium based compounds. However, Pt(II) and Rh(III) have been reported by A. Sabel, J. Smidt, R. Jira and H. Prigge, Chem. Ber., 102, pp 2939-2950 (1969), to catalyze the reaction. In addition, Young, U.S. Pat. No. 3,755,387, patented Aug. 26, 1973, entitled: "A Vapor Phase Transvinylation Process", claims the use of supported Hg, Pd, Pt, Ir, Rh, Ru or Os salt catalysts in a vapor phase transvinylation process. The experimental portion discloses the use of only palladium on carbon, copper on carbon, iron on carbon, palladium/copper on carbon, palladium/copper/iron on silica, mercuric acetate on carbon, and mercuric chloride on carbon. Hg and Pd are cited, at col. 1, line 67, as the preferred metals.
Mercury and palladium based catalysts are not, however, entirely satisfactory. Mercury-based catalysts are toxic, undesirably volatile, and are typically activated with sulfuric acid to promote reaction and then deactivated by neutralization with base prior to product distillation. Traces of adventitious free acid generated by this system tend to promote ethylidene diester formation. Mercury-based catalysts are not thermally stable at elevated temperatures and often deactivate forming metallic mercury.
Palladium-based catalysts are not sufficiently thermally stable to allow product removal by distillation at elevated temperatures. Such catalysts often deactivate forming metallic Pd.
More recently, it has been discovered that ruthenium compositions are useful transvinylation catalysts for numerous Bronsted acids and derivatives of Bronsted acids as disclosed in U.S. Pat. No. 4,981,973, and assigned to the assignee of the present application. The invention disclosed therein relates to a process for the transvinylation of a vinyl derivative of a first Bronsted acid with a second Bronsted acid which comprises providing a liquid phase mixture containing the vinyl derivative of the first Bronsted acid and the second Bronsted acid in the presence of a ruthenium compound at a temperature at which transvinylation occurs, and recovering as a product of transvinylation the vinyl derivative of the second Bronsted acid. The beneficial use of ruthenium-containing compounds as catalysts for transvinylation processes overcomes several deficiencies noted for other catalysts that had been used in transvinylation processes.
The ruthenium based transvinylation catalysts have substantial benefits over the mercury and palladium-based catalysts. The ruthenium-based catalysts are soluble, non-volatile, possess high thermal stability and exhibit high catalytic activity at elevated temperatures. Unlike palladium, ruthenium-based catalysts do not lead to observable metal precipation, even at elevated reaction temperatures, such as above 150.degree. C.
Transvinylation, principally for economic reasons, preferably utilizes inexpensive vinyl reactant feedstocks such as vinyl acetate. Conventionally, with vinyl acetate as the reactant feedstock, the prior art teaches a sequence involving transvinylation followed by distillation of the transvinylation reaction mixture to recover the vinyl product ester. For example, even in early art using mercury catalysts, such as U.S. Pat. No. 2,245,131, vinyl acetate and benzoic acid were first transvinylated using a mercury/sulfuric acid catalyst under reflux, and then the volatiles were removed by distillation prior to distillation to recover vinyl benzoate. Further, if distillation is conducted in the presence of a transvinylation catalyst which is active at the kettle temperature, product reversion to reactant can lower overall yield.
Reactive distillation is a well known processing technique. In reactive distillation, distillation is used to control the concentrations of species present in the reaction zone to speed up the reaction and to improve selectivity. The simultaneous reaction and distillation operation is advantageous. Benefits of reactive distillation include efficient utilization of equipment, reduced residence time requirement for reaction and reduced side products. In reversible reactions, continuous removal of one or more of the products from the reaction zone reduces the reaction rate for the reverse reaction and thereby increases the net rate of the conversion of feed to product.
Reactive distillation has been applied to reactions in which the products are the most volatile component in the system. In those situations, products are removed from the column overhead. For example U.K. Patent No. 1,486,443 describes a transvinylation reaction for the production of a vinyl ester of an organic carboxylic acid by transvinylating a vinyl ester of an organic carboxylic acid with an organic carboxylic acid whose vinyl ester has a lower boiling point than the vinyl ester reactant. Because the boiling point of the vinyl ester reactant is higher than the boiling point of the vinyl ester product, it is stated that separation of the lower boiling point, more volatile product from the higher boiling point, less volatile reactant is facilitated as the reaction proceeds.
However, reactive distillation has not been used heretofore in chemical reactions including equilibrium reactions where the reactants have a lower boiling point than the reaction products that are to be removed and are thus more volatile than the reaction products. When the reactants are the most volatile components in the system, distillation results in the removal of the reactants and in the accumulation of products. The accumulation of products is undesirable, especially in equilibrium reactions due to the adverse effect, that is, the reverse reaction leading to the production of the reactants. More specifically, reactive distillation for transvinylation reactions has been disclosed only where the vinyl product ester is more volatile than the vinyl reactant ester. Reactive distillation for transvinylation reactions has thus followed conventional techniques whereby the more volatile product component is removed as the reaction progresses.
Thus, despite the generally recognized advantages of reactive distillation and the prior art transvinylation processes using reactive distillation in transvinylation reactions where the vinyl product ester is more volatile than the vinyl reactant ester, reactive distillation has not been disclosed heretofore for use in transvinylation processes where the vinyl product ester is less volatile than the vinyl reactant ester. Accordingly, the benefits of reactive distillation have not been realized in such transvinylation processes.